I recently did an emerge -depclean and just wanted to make sure everything is ok, so I tried emerge -uDNvp world and revdep-rebuild -i -pv - nothing to do, everything ok.
But when I say emerge -e world -pv (just for fun, I'm not going to do it) it wants to update 4 packages. Checking them it reveals they really have updates available. Trying to emerge one of the packages in question (emerge app-arch/rpm2targz -pv) reveals the update, too.

Does anyone have an answer to my question what the cause of this effect is?